High-temperature oxidation-resistant cobalt base alloys



United States Patent 3,202,506 HIGH-TEMPERATURE @XIDATEEENRESISTANT CBEALT Efifih. ALLUYg David E. Deutsch, Walnut 'Creelt, (falii, assignor, by niesne assignments, to the United States of America as represented by the United States Atomic Energy (Ionimission No Drawing. Fiied L on. 23, 1063, $52. No. 253,511 10 Claims. (Cl. 75-171) The invention relates in general to high-temperature, oxidation-resistant alloys and, more particularly, to alloys 3,202,50b Patented Aug. 2%, i965 TABLE Alloy Class Cr W Ta- Nb Mo 0 Y Go 6 to 12%-.. 0.30 to 1.25% 0.05 to 2 Balance. 0.5 to 12%, 0.30 to1.25%-- 0.05 to 2 5% D0. -i 2 to 0.40 to 1.3%. 0.05 to 2 59 D0.

(*) C) 0.30 to 1.25% 0.05 to 2 5% *Perccntages by weight:

comprising a basic alloy of cobalt with lesser proportions of alloying agents including minor proportions of yttrium to enhance oxidation resistance and improve other properties.

High-temperature, metallic alloys including those containing cobalt are extensively utilized where hardness and high strength at high temperatures is required. A principal use is in the fabrication of jet engine turbine blades, supercharger parts, and the like. In such applications, a serious limitation is the unsatisfactory oxidation resistance of usual alloys as well as the poor retention of physical properties, wherefore maximum operating conditions are below those at which optimum or improved efficiencies can be achieved.

It has now been found that the addition of minor proportions of yttrium of up to about 2.5% by weight to a cobalt base alloy results in a remarkable improvement in the oxidation resistance of the alloy. Such cobalt base alloy generally comprises somewhat more than 50% cobalt, of the order of -24% chromium, 6-l2% tungsten, with minor proportions of carbon and varied amounts of tantalum, columbium, or molybdenum. The alloys possess high strength at 1800 F., moderate strength at 2000" F., and exceptional oxidation resistance at 2300 F.

Accordingly, it is an object of the invention to provide high-temperature, oxidation-resistant metallic alloys.

Another object of the invention is to provide a cobalt base alloy to which yttrium is added to increase the oxidation resistance and improve the high-temperature properties thereof.

Still another object of the invention is to provide a metallic alloy including a mixture of cobalt together with chromium and tungsten, comprising a basic mixture to which yttrium is added in minor proportions to increase oxidation resistance and improve the high-temperature properties thereof.

A further object of the invention is to provide a metallic alloy including a mixture of cobalt together with chromium and tungsten, comprising a basic alloy mixture with varied amounts of tantalum, columbium, or molybdenum, to which minor proportions of yttrium is added to improve oxidation resistance and other high-temperature properties.

Other objects and advantages of the invention will be apparent in the following description of the invention.

Alloys of the character described containing about 10% tungsten or about 10% tantalum are considered superior for turbo-jet and ram-jet application and are accordingly especially preferred. Inclusion amounts, e.g., less than 0.05% of other materials, such as silicon, manganese, boron, and phosphorous, may be present without materially affecting final properties. Commercial production of the alloys, however, would undoubtedly introduce additional impurities comprising Without serious detriment:

Percent Ni O-l Fe 0-2 Mn 01.5 Si 0-1 B 001-0 15 air 0.01-0 50 The alloy may be prepared by melting the constituents in a vacuum or inert-atmosphere furnace using a suitable high-temperature crucible or the like. Product articles may be produced by casting techniques with as cast articles and test specimen exhibiting quite desirable properties. Such alloys characteristically exhibit high strength, i.e., tensile strength of above about 40,000 psi. at 1800 F. and moderate strength at about 2000 F. Moreover, the oxidation resistance at temperatures of the order of 2300" F. is outstanding. The mechanism whereby yttrium promotes oxidation resistance is not fully understood; however, the phenomenon appears to be related to the high free-energy value for the formation of yttrium oxide resulting in the formation of an extremely stable oxide coating on exposed surfaces. It can be theorized that yttrium also diffuses into the scale of the oxidized alloys to create an ordered, saturated, spinal-type structure in the scale. Such a type of spinel is known to provide oxidation resistance by minimizing or preventing the diffusion of oxygen or other gases through the scale coating. Yttrium also promotes reasonable ductility at high strength levels by immobilizing gaseous and interstitial impurities. No special methods of alloying or fabrication are required. The methods used for melting, casting and fabrication of refractory metals in conventional practice are suitable.

Further details of the invention will be apparent in the following illustrative examples:

Example I An alloy of Class I was prepared by melting the alloy constituents in a vacuum induction furnace using a beryllia crucible. The alloying materials were utilized in the following Weight-percentage proportions: 21.2% chromium, 9.8% tungsten; 9.4% tantalum, 0.18% carbon; 1.34% yttrium; and the balance being cobalt. Silicon, manganese, boron, and phosphorous were present in amounts of less than 0.02%

Tensile testing specimens were prepared by casting in Example II The preferred composition of this class of alloy, i.e., Class 11 consists of the following weight-percentage proportions: 22.3% chromium, 9.5% tungsten, 10.2% niobium, 0.76% carbon, and 0.90% yttrium; the balance being 'cobalt. Silicon, manganese, boron, and phosphorous should be present in amounts less than 0.05%. The method of production and testingis the same as in Example I. The properties of this alloy should be comparable in strength and oxidation resistance to Example I.

Example 111 The preferred composition of this class of alloy, i.e., Class III consists of the following weight-percentage proportions: 21.1% chromium, 10.2% tungsten, 8.0% molybdenum, 0.60% carbon, and 1.1% yttrium; the balance being cobalt. Silicon, manganese, boron, and phosphorous would be present in amounts less than 0.03%.

The procedure for producing and testing this alloy is the same as inExample I. This alloy should likewise be lar in properties to Example I.

7 While there has been described in the foregoing what may be considered to be preferred embodiments of the invention modifications may be made therein without desimi to 2.5% by wt. of yttrium and the remainder being cobalt.

2. The alloy as defined in claim 1, wherein the material selected from said group is tantalum in an amount in the range of '6 to 12% by wt. I

3. The alloy as defined in claim 1 wherein the material selected from said group is niobium in an amount in the range of 0.5 to 12% by wt.

4. The alloy as defined in claim 1 wherein the material selected from said group is molybdenum in an amount in the range of2 to 10% by Wt.

5. The alloy as defined in claim 1 wherein the material selected from said group is an admixture of tantalum, niobium and molybdenum in an aggregate amount in the range of 7 to 12% by Wt.

6. The alloy as defined in claim 1 wherein the material selected from said group is an admixture of tantalum and molybdenum in an aggregate amount in the range of 7-12% by wt.

7. The alloy as defined in clairni 1 wherein the material selected from said group is an admixture of niobium and molybdenum in an aggregate amount in the range of V 7to12% by wt. I

parting from the teachings of the invention and it is intended to cover all such as fall within the scope of the appended claims.

What is claimed is:

1. A cobalt base alloy consisting essentially of 15 to 24% by wt. of chromium, 6 to 12% by wt. of tungsten, up to a maximum of 12% by wt. of at least one material selected from the group consisting of tantalum, niobium 5 and molybdenum, 0.30 to 1.25% by Wt. of carbon, 0.05

8. A cobalt base alloy having enhanced oxidation resistance and other improved high temperature properties consisting essentially of about 21% by wt. of chromium, about 10% by wt. of tungsten, about 10% by Wt. of tantalum, about 0.2% by wt. of carbon and about 1.3% by wt. of yttrium with the remainder being cobalt.

9. A cobalt base alloy having enhanced oxidation resistance and other improvedhigh temperature properties consisting essentially of about 22%. by wt. of chromium, 10% by wt. of tungsten, 10% by wt. of niobium, 0.75% by wt. of carbon and 0.9% by wt. of yttrium with the remairlder being cobalt.

10. A cobalt base alloy having enhanced oxidation resistance and other improved high temperature properties consisting essentially of 21% by wt. of chromium, 10% by wt. of tungsten, 8% by wt. of molybdenum, 0.6% by wt. of carbon and 1.1% by Wt. of yttrium with the remainder being cobalt.

References Cited by the Examiner UNITED STATES PATENTS 2,030,342 2/36 Wissler -171 2,247,643 7/41 Rohn et al. 75-171 2,304,353 12/42 Griffiths et al. 75-171 2,486,576 11/49 Savage 75-171 2,515,774 7/50 Johnson 75-171 2,974,036 3/61 Thielemann 75-171 3,017,265 l/ 62 McGurty et al. 75-176 X 3,026,199 3/62 'Thielemann 75-171 DAVID L. RECK, Primary Examiner.

ROGER L. CAMPBELL, WINSTON A. DOUGLAS,

. Examiners. 

1. A COBALT BASE ALLOY CONSISTNG ESSENTIALLY OF 15 TO 24% BY WT. OF CHROMIUM, 6 TO 12% BY WT OF TUNGSTEN, UP TO A MAXIMUM OF 12% BY WT OF AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF TANTALUM, NIOBIUM AND MOLYBDENUM, 0.30 TO 1.25% BY WT OF CARBON, 0.05 TO 2.5% BY WT OF YTTRIUM AND THE REMAINDER BEING COBALT. 